[GDScript] Prevent some vararg methods binding arguments to member variables

[AThousandShips]

Calling some methods from GDScript with member variable arguments causes the pointer to that argument being passed instead of the value, affects:

• Signal.emit
• Object.emit_signal
• SceneTree.call_group/_flags

Tried a separate method that's possibly more secure, by copying arguments into temporaries if they are member variables, this is a bit hit and miss and had some problems applying them just for vararg methods, this problem doesn't really affect other cases significantly either as most of the time it doesn't cause this kind of chain effect, so I feel this is more of a targeted situation where we can just fix it in the places where it's needed, instead of hitting every method called with a member variable with a temporary

I only added these fixes to the bound methods, so it won't affect calls from c++ normally, like Signal.emit, but instead the bound method under variant_call

Note also that the ptrcall methods in Variant use temporary storage for variants, and these are called from extensions AFAIK, so there's precedent for this solution

The immediate, indiscriminate solution (as I couldn't reliably test for vararg, and therefore would miss some cases) would have been:

diff --git a/modules/gdscript/gdscript_compiler.cpp b/modules/gdscript/gdscript_compiler.cpp
index 13ed66710c..5a9a5b2264 100644
--- a/modules/gdscript/gdscript_compiler.cpp
+++ b/modules/gdscript/gdscript_compiler.cpp
@@ -614,6 +614,11 @@ GDScriptCodeGenerator::Address GDScriptCompiler::_parse_expression(CodeGen &code
                                if (r_error) {
                                        return GDScriptCodeGenerator::Address();
                                }
+                               if (arg.mode == GDScriptCodeGenerator::Address::MEMBER) {
+                                       GDScriptCodeGenerator::Address temp = codegen.add_temporary(arg.type);
+                                       gen->write_assign(temp, arg);
+                                       arg = temp;
+                               }
                                arguments.push_back(arg);
                        }

This is a bit brute force, but it works as well

• Fixes: Parameter emitted with a signal references member variable instead of passed Variant #88885

[AThousandShips]

Can't test the other methods here AFAIK as groups don't work in the testing, unless I'm mistaken

[RandomShaper]

Allocations here are are too bad for performance. I'd suggest using alloca().

[AThousandShips]

Will do, wasn't well versed in using it when I wrote this one

[AThousandShips]

Added everywhere, might not be as relevant to the variant call one but shouldn't hurt

[AThousandShips]

Using the same method as used in:

• [Core] Disconnect one-shot signals before calling callbacks #89451